1. Field of the Invention
This invention relates to a method for reading signals from plural elements simultaneously, and is particularly usable for radiation ray measurement using an imaging type super high energy-resolution X-ray detector and thermal measurement using an imaging type super sensitive infrared detector.
2. Description of the Prior Art
Microcalorimeters are employed as super high energy-resolution X-ray detectors or highly sensitive infrared detectors. Recently, it has been proposed to use microcalorimeters as imaging elements of X-ray or infrared cameras of an astronomical observatory orbiting in space. At present, the camera is composed of plural microcalorimeters, and the signals of each microcalorimeter are read out independently.
In this case, a microcalorimeter requires multiple wires to apply a bias voltage and multiple wires to read out signals.
On the other hand, a microcalorimeter is usually operated at a very low temperature of about 0.1 to 4.2 K. Therefore, a camera requires that many wires be drawn out from the camera situated at a very low temperature to measurement electronics situated at room temperature. As a result, conventional microcalorimeter cameras have only tens of imaging elements, and thus the effective field of view is restricted. Thus multiple camera pointings are required to observe spatially extended objects.
To solve this problem, attempts have been made to switch and read out signals from plural microcalorimeters in sequence using SQUIDs at high switching speeds. Such a technique enables read out signals from plural microcalorimeters by a pair of cables and increases the field of view of the camera. However, there are many technical problems associated with such high speed switching of SQUIDs, and, thus, there are practical limits to applications of the above-mentioned technique.
It is an object of the present invention to provide a method for reading signals from plural microcalorimeters at once without providing many wires between low temperature sensor stage and room temperature measurement electronics.
For achieving the above object, this invention relates to a method for reading signals from plural elements simultaneously, comprising the steps of providing plural elements and composing plural element groups of the elements, driving the element groups by AC biases having their respective different frequencies, adding signals from the elements belonging to their respective different element groups, and taking out on one signal line and reading a multiplex signal composed of the thus added signals.
In a preferred embodiment of the present invention, plural elements are arranged in nxc3x97m matrix to compose plural element groups. Each element group is composed of n elements arranged in a column. Then, the element groups are driven by AC biases having their respective different frequencies, and the signals from the elements belonging to their respective different element groups are added at every line. Then, a multiplex signal composed of the thus added signals is taken out on one signal line and read.
In the signal reading method of the present invention, AC biases of different frequencies are applied to their respective element groups. That is, a different AC bias is superimposed as a carrier signal on the elements of every element group. Therefore, when the signals from corresponding elements of every element group are added, a multiplex signal can be obtained from all of the element groups in a frequency space. Moreover, according to the present invention, the multiplex signal is taken out on one signal line, i.e., the multiplex signal can be obtained by using only one signal line. As a result, signals from plural elements can be read simultaneously in the absence of separate wires for each of the respective elements.
In the case of an application of AC biases of relatively large amplitudes in the presence of relatively small signals obtained from the elements, the superposition of the AC biases on the signals may result in cancellation of the signals obtained from the elements. Therefore, it is desired that each element be set in a bridge-type circuit so that the amplitudes of the AC biases can be effectively reduced, and the signals obtained from the elements can be taken out precisely.